1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device which can reduce contact resistance.
2. Description of the Related Art
In a semiconductor memory device, a cell selection signal is applied to a word line and a data signal is applied to a bit line, so that the data signal is applied to the selected cell. The bit line is in contact with the word line in the periphery region of the memory device. The word line and the bit line are formed to materials having good conductivity, for preventing signal delay. For example, they are generally formed to a tungsten polycide structure in which a tungsten silicide layer is formed on a doped polysilicon layer.
FIG. 1A and FIG. 1B are cross sectional views for describing a conventional method of forming contact between a word line and a bit line in the periphery region of a memory device.
Referring to FIG. 1A, a word line 12 in which a first tungsten silicide (WSix) layer 12b is formed on a first doped polysilicon layer 12a is formed on a semiconductor substrate 10. An intermediate insulating layer 14 is then formed on the overall substrate and etched to expose the portion of the surface of the first tungsten silicide layer 12b of the word line 12, thereby forming a contact hole 16. Thereafter, a second doped polysilicon 18a and a second tungsten silicide layer 18b as materials for a bit line 18 are sequentially formed on the surface of the contact hole 16 and on the intermediate insulating layer 14, as shown in FIG. 1B.
When forming the contact hole 16, plasma gas such as C.sub.x F.sub.y, CF.sub.4 +O.sub.2, CH.sub.x Br.sub.y is used as an etching gas. However, owing to the ion bombardment of the plasma gas, the surface crystal structure for the exposed first tungsten silicide layer 12b of the word line 12 is transformed into an amorphous and/or quasi-stable state, to increase contact resistance between the word line 12 and the bit line 18.
Furthermore, owing to the bonding force difference between W--Si and Si--Si in the first tungsten silicide layer 12b, sputtering yield difference increases. Therefore, as shown in FIG. 1A, the exposed surface of the first tungsten silicide layer 12b is roughed, so that contact resistance between the word line 12 and the bit line 18 further increases and contact interface therebetween is unstablized.
Moreover, the plasma gas reacts with W and/or Si of the first tungsten silicide layer 12b, so that processing productions 100 having negative .DELTA.H as shown in TABLE 1 are created on the exposed surface of the first tungsten silicide layer 12b, and acts as factor increasing the contact resistance.
TABLE 1 processing productions .DELTA. H(KJ/mole) WC, SiC -20.5 SiO.sub.2 -17 WNx -12.6 W.sub.2 N -72 WO.sub.2 -533 WO.sub.3 -843